Thank you for your advice, the model does not diverge yet. But it runs very slowly, and it seems no condensation occurs at the cold wall. Unfortunately, I could not attach picture from the results (the data file was lost I do not know why), but the steam began accumulate at the top. I set the condensation frequency from 0.1 to 1000 but it had no effect. The time is only 0.5 s, but the model has run 16 hours. Should it run for a week or is there any mistake I make? Thank you for your help!